We have 4 Anconas. Recently, a neighbour's duck showed up in the yard and started hanging around with my four. Not sure what kind it is. After a couple of days they were all walking, swimming and eating together. She wanted in the pen at night so we let her. The neighbor has no concern about where their duck is. My question: is it okay to just let this duck join our group? Are there any signs I should be looking for that tells me things are not okay with her being with us? She hasn't been aggressive with us, the dogs or the ducks.